Summary of Critical and Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) community investment partnership shares	Dec. 31, 2016 USD ($) property community shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Principles of Consolidation [Abstract]
Noncontrolling interest in Operating Partnership	3.30%	3.30%
Real Estate Rental Properties [Abstract]
Threshold useful life of assets for capitalization	1 year
Depreciable life of various categories of fixed assets [Abstract]
Acquired in-place lease value, net	$ 400,000	$ 1,400,000
Number of communities held-for-sale | community	0	1
Revenues and Gains on Sale of Real Estate [Abstract]
Lease terms, minimum	6 months
Lease terms, maximum	12 months
Cash Equivalents and Restricted Cash [Abstract]
Original maturities of highly liquid investments to be classified as cash equivalents, maximum	3 months
Marketable Securities [Abstract]
Maturity date of investments in mortgage backed securities, first	November 2019	November 2019
Maturity date of investments in mortgage backed securities, final	September 2020	September 2020
Available-for-sale Securities [Abstract]
Available for sale - Carrying Value	$ 190,004,000	$ 139,189,000
Held-to-maturity Securities [Abstract]
Total marketable securities and other investments, Amortized Cost	187,155,000	137,715,000
Total marketable securities and other investments, Gross Unrealized Gain (Loss)	2,849,000	1,474,000
Total marketable securities and other investments, Carrying Value	190,004,000	139,189,000
Proceeds from sale of available-for-sale securities	35,500,000	30,500,000	$ 3,300,000
Gain on sale of available-for-sale securities	1,900,000	5,700,000	0
Sale of other investments	0	0	5,600,000
Gain on sale of other investments			600,000
Capitalization Policy [Abstract]
Capitalized internal costs related to development and redevelopment projects	20,300,000	18,500,000	17,600,000
Fair Value of Financial Instruments [Abstract]
Fixed rate debt carrying amount	4,900,000,000	5,100,000,000
Fixed rate debt fair value	5,000,000,000	5,100,000,000
Variable rate debt, carrying amount	792,900,000	499,700,000
Variable rate debt fair value	793,900,000	502,800,000
Mortgage backed securities fair value	120,700,000	$ 108,800,000
Investments, Owned, Federal Income Tax Note [Line Items]
Number of properties disposed | property		2
Deferred tax expense on gain on sale of real estate and land	0	$ 4,410,000	0
Tax act, deferred tax liability, net tax benefit	1,500,000
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	6,192,178,000
Other comprehensive income before reclassification	27,810,000
Amounts reclassified from accumulated other comprehensive loss	(14,158,000)
Other comprehensive income	13,652,000
Stockholders' equity, ending balance	$ 6,277,406,000	6,192,178,000
Number of consolidated co-investments that now meet the definition of a VIE | investment	8
Number of DownREIT limited partnerships the company consolidates | partnership	16
Number of communities within the DownREIT partnership | community	8
Assets related to variable interest entities, net intercompany eliminations	$ 837,700,000	746,100,000
Liabilities related to variable interest entities, net of intercompany eliminations	265,500,000	221,300,000
Noncontrolling interests in VIEs	$ 66,700,000	$ 45,400,000
Total DownREIT units outstanding (in shares) | shares	917,593	952,140
Redemption value of the variable interest entities	$ 221,500,000	$ 221,400,000
Redeemable noncontrolling interest	39,206,000	44,684,000	$ 45,452,000	$ 23,256,000
Noncontrolling interest in limited partnerships	$ 32,400,000	18,600,000
Computer software and equipment [Member] | Minimum [Member]
Depreciable life of various categories of fixed assets [Abstract]
Depreciable life, average	3 years
Computer software and equipment [Member] | Maximum [Member]
Depreciable life of various categories of fixed assets [Abstract]
Depreciable life, average	5 years
Interior apartment home improvements [Member]
Depreciable life of various categories of fixed assets [Abstract]
Depreciable life, average	5 years
Furniture, fixtures and equipment [Member] | Minimum [Member]
Depreciable life of various categories of fixed assets [Abstract]
Depreciable life, average	5 years
Furniture, fixtures and equipment [Member] | Maximum [Member]
Depreciable life of various categories of fixed assets [Abstract]
Depreciable life, average	10 years
Land improvements and certain exterior components of real property [Member]
Depreciable life of various categories of fixed assets [Abstract]
Depreciable life, average	10 years
Real estate structures [Member]
Depreciable life of various categories of fixed assets [Abstract]
Depreciable life, average	30 years
Accumulated other comprehensive loss, net [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	$ (32,098,000)
Stockholders' equity, ending balance	(18,446,000)	(32,098,000)
Change in Fair Value and Amortization of Swap Settlements [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(32,963,000)
Other comprehensive income before reclassification	24,634,000
Amounts reclassified from accumulated other comprehensive loss	(12,312,000)
Other comprehensive income	12,322,000
Stockholders' equity, ending balance	(20,641,000)	(32,963,000)
Unrealized Gains on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	865,000
Other comprehensive income before reclassification	3,176,000
Amounts reclassified from accumulated other comprehensive loss	(1,846,000)
Other comprehensive income	1,330,000
Stockholders' equity, ending balance	2,195,000	865,000
Investment-grade unsecured bonds [Member]
Available-for-sale Securities [Abstract]
Available for sale - Amortized Cost	4,365,000
Available for sale - Gross Unrealized Gain (Loss)	(40,000)
Available for sale - Carrying Value	4,325,000
Investment funds - debt securities [Member]
Available-for-sale Securities [Abstract]
Available for sale - Amortized Cost	27,914,000	19,604,000
Available for sale - Gross Unrealized Gain (Loss)	(29,000)	(73,000)
Available for sale - Carrying Value	27,885,000	19,531,000
Investment funds - U.S. treasuries [Member]
Available-for-sale Securities [Abstract]
Available for sale - Amortized Cost	10,999,000	10,022,000
Available for sale - Gross Unrealized Gain (Loss)	(55,000)	(22,000)
Available for sale - Carrying Value	10,944,000	10,000,000
Common stock and stock funds [Member]
Available-for-sale Securities [Abstract]
Available for sale - Amortized Cost	34,329,000	13,696,000
Available for sale - Gross Unrealized Gain (Loss)	2,973,000	1,569,000
Available for sale - Carrying Value	37,302,000	15,265,000
Mortgage backed securities [Member]
Held-to-maturity Securities [Abstract]
Held to maturity - Amortized Cost	109,548,000	94,393,000
Held to maturity - Gross Unrealized Gain (Loss)	0	0
Held to maturity - Carrying Value	$ 109,548,000	$ 94,393,000
Common stock and stock funds [Member]
Status of cash dividends distributed [Abstract]
Ordinary income	84.04%	86.68%	99.28%
Capital gains	13.20%	7.11%	0.72%
Unrecaptured section 1250 capital gain	2.76%	6.21%	0.00%
Total cash dividends distributed	100.00%	100.00%	100.00%
Series H Preferred Stock [Member]
Status of cash dividends distributed [Abstract]
Ordinary income	0.00%	86.68%	99.28%
Capital gains	0.00%	7.11%	0.72%
Unrecaptured section 1250 capital gain	0.00%	6.21%	0.00%
Total cash dividends distributed	0.00%	100.00%	100.00%
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Pro Forma [Member] | Accounting Standards Update 2017-05 [Member] | Retained Earnings [Member]
Property, Plant and Equipment [Line Items]
Cumulative adjustment to retained earnings		$ 123,700,000
Essex Portfolio, L.P. [Member]
Investments, Owned, Federal Income Tax Note [Line Items]
Deferred tax expense on gain on sale of real estate and land	$ 0	4,410,000	$ 0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Other comprehensive income before reclassification	28,761,000
Amounts reclassified from accumulated other comprehensive loss	(14,642,000)
Other comprehensive income	14,119,000
Redeemable noncontrolling interest	39,206,000	44,684,000
Essex Portfolio, L.P. [Member] | Accumulated other comprehensive loss, net [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(29,348,000)
Stockholders' equity, ending balance	(15,229,000)	(29,348,000)
Essex Portfolio, L.P. [Member] | Change in Fair Value and Amortization of Swap Settlements [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	(30,161,000)
Other comprehensive income before reclassification	25,477,000
Amounts reclassified from accumulated other comprehensive loss	(12,733,000)
Other comprehensive income	12,744,000
Stockholders' equity, ending balance	(17,417,000)	(30,161,000)
Essex Portfolio, L.P. [Member] | Unrealized Gains on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Stockholders' equity, beginning balance	813,000
Other comprehensive income before reclassification	3,284,000
Amounts reclassified from accumulated other comprehensive loss	(1,909,000)
Other comprehensive income	1,375,000
Stockholders' equity, ending balance	$ 2,188,000	$ 813,000